-
+
Full Text Search
as a sorted array of normalized lexemes. Along with the lexemes it is
often desirable to store positional information to use for
proximity ranking, so that a document that
- contains a more dense region of query words is
+ contains a more dense region of query words is
assigned a higher rank than one with scattered query words.
SELECT ts_headline('english',
'The most common type of search
-is to find all documents containing given query terms
+is to find all documents containing given query terms
and return them in order of their similarity to the
query.',
to_tsquery('query & similarity'));
ts_headline
------------------------------------------------------------
- containing given <b>query</b> terms
+ containing given <b>query</b> terms
and return them in order of their <b>similarity</b> to the
<b>query</b>.
is to find all documents containing given query terms
and return them in order of their similarity to the
query.',
- to_tsquery('query & similarity'),
+ to_tsquery('query & similarity'),
'StartSel = <, StopSel = >');
ts_headline
-------------------------------------------------------
(notice that one token can produce more than one lexeme)
+
+ a single lexeme with the TSL_FILTER flag set, to replace
+ the original token with a new token to be passed to subsequent
+ dictionaries (a dictionary that does this is called a
+ filtering dictionary)
+
+
an empty array if the dictionary knows the token, but it is a stop word
until some dictionary recognizes it as a known word. If it is identified
as a stop word, or if no dictionary recognizes the token, it will be
discarded and not indexed or searched for.
+ Normally, the first dictionary that returns a non-NULL
+ output determines the result, and any remaining dictionaries are not
+ consulted; but a filtering dictionary can replace the given word
+ with a modified word, which is then passed to subsequent dictionaries.
+
+
The general rule for configuring a list of dictionaries
is to place first the most narrow, most specific dictionary, then the more
general dictionaries, finishing with a very general dictionary, like
+ A filtering dictionary can be placed anywhere in the list, except at the
+ end where it'd be useless. Filtering dictionaries are useful to partially
+ normalize words to simplify the task of later dictionaries. For example,
+ a filtering dictionary could be used to remove accents from accented
+ letters, as is done by the
+ contrib/unaccent
+ extension module.
+
+
Stop Words
Here, english is the base name of a file of stop words.
The file's full name will be
$SHAREDIR/tsearch_data/english.stop,
- where $SHAREDIR means the
+ where $SHAREDIR means the
PostgreSQL installation's shared-data directory,
often /usr/local/share/postgresql (use pg_config
--sharedir to determine it if you're not sure).
asciiword | Word, all ASCII | Paris | {my_synonym,english_stem} | my_synonym | {paris}
-
+
- An asterisk (*) at the end of definition word indicates
- that definition word is a prefix, and to_tsquery()
- function will transform that definition to the prefix search format (see
- ).
- Notice that it is ignored in to_tsvector().
+ The only parameter required by the synonym template is
+ SYNONYMS, which is the base name of its configuration file
+ — my_synonyms in the above example.
+ The file's full name will be
+ $SHAREDIR/tsearch_data/my_synonyms.syn
+ (where $SHAREDIR means the
+
PostgreSQL installation's shared-data directory).+ The file format is just one line
+ per word to be substituted, with the word followed by its synonym,
+ separated by white space. Blank lines and trailing spaces are ignored.
+
+
+ The synonym template also has an optional parameter
+ CaseSensitive, which defaults to false. When
+ CaseSensitive is false, words in the synonym file
+ are folded to lower case, as are input tokens. When it is
+ true, words and tokens are not folded to lower case,
+ but are compared as-is.
- Contents of $SHAREDIR/tsearch_data/synonym_sample.syn:
+ An asterisk (*) can be placed at the end of a synonym
+ in the configuration file. This indicates that the synonym is a prefix.
+ The asterisk is ignored when the entry is used in
+ to_tsvector(), but when it is used in
+ to_tsquery(), the result will be a query item with
+ the prefix match marker (see
+ ).
+ For example, suppose we have these entries in
+ $SHAREDIR/tsearch_data/synonym_sample.syn:
postgres pgsql
postgresql pgsql
gogle googl
indices index*
-
-
- Results:
+ Then we will get these results:
-=# CREATE TEXT SEARCH DICTIONARY syn (template=synonym, synonyms='synonym_sample');
-=# SELECT ts_lexize('syn','indices');
+mydb=# CREATE TEXT SEARCH DICTIONARY syn (template=synonym, synonyms='synonym_sample');
+mydb=# SELECT ts_lexize('syn','indices');
ts_lexize
-----------
{index}
(1 row)
-=# CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);
-=# ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;
-=# SELECT to_tsquery('tst','indices');
+mydb=# CREATE TEXT SEARCH CONFIGURATION tst (copy=simple);
+mydb=# ALTER TEXT SEARCH CONFIGURATION tst ALTER MAPPING FOR asciiword WITH syn;
+mydb=# SELECT to_tsvector('tst','indices');
+ to_tsvector
+-------------
+ 'index':1
+(1 row)
+
+mydb=# SELECT to_tsquery('tst','indices');
to_tsquery
------------
'index':*
(1 row)
-=# SELECT 'indexes are very useful'::tsvector;
+mydb=# SELECT 'indexes are very useful'::tsvector;
tsvector
---------------------------------
'are' 'indexes' 'useful' 'very'
(1 row)
-=# SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
+mydb=# SELECT 'indexes are very useful'::tsvector @@ to_tsquery('tst','indices');
?column?
----------
t
(1 row)
-
-=# SELECT to_tsvector('tst','indices');
- to_tsvector
--------------
- 'index':1
-(1 row)
-
- The only parameter required by the synonym template is
- SYNONYMS, which is the base name of its configuration file
- — my_synonyms in the above example.
- The file's full name will be
- $SHAREDIR/tsearch_data/my_synonyms.syn
- (where $SHAREDIR means the
-
PostgreSQL installation's shared-data directory).- The file format is just one line
- per word to be substituted, with the word followed by its synonym,
- separated by white space. Blank lines and trailing spaces are ignored.
-
-
- The synonym template also has an optional parameter
- CaseSensitive, which defaults to false. When
- CaseSensitive is false, words in the synonym file
- are folded to lower case, as are input tokens. When it is
- true, words and tokens are not folded to lower case,
- but are compared as-is.
-
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